Principles of Image Resolution Flashcards

A 5 MHz transducer in soft tissue (c = 1540 m/s) produces a wavelength of approximately:

Answer: 0.31 mm

λ = c/f = 1540/5,000,000 ≈ 0.308 mm ≈ 0.31 mm.

Which statement correctly compares axial and lateral resolution at a specific depth?

Answer: Axial resolution is typically better than lateral resolution

Axial resolution (determined by SPL) is generally superior to lateral resolution because the beam width is almost always wider than the SPL.

Coded excitation (e.g., chirp pulses) is used in ultrasound primarily to:

Answer: Improve signal-to-noise ratio and penetration while maintaining resolution

Coded excitation transmits a long modulated pulse and uses pulse compression on receive to achieve high SNR with good axial resolution.

Spatial compounding improves image quality by:

Answer: Averaging frames from multiple steering angles to reduce speckle and improve contrast resolution

Compounding averages images steered from several angles, reducing coherent speckle and improving contrast and boundary definition.

Which parameter does NOT directly affect axial resolution?

Answer: Active aperture width

Active aperture width affects lateral resolution (beam width), not axial resolution, which depends solely on spatial pulse length.

The depth of field (depth of focus) of an ultrasound beam refers to:

Answer: The range of depths over which lateral resolution remains acceptable

Depth of field describes the axial extent around the focal point where lateral resolution stays within an acceptable limit.

Which approach can improve both axial resolution and penetration simultaneously in modern ultrasound?

Answer: Broadband multi-frequency transducers combined with coded excitation

Broadband transducers with coded excitation allow penetration at lower frequencies while compressing the pulse for good axial resolution.